This invention relates to magnetic refrigeration and more particularly to low temperature refrigeration between 4 and about 20 K. with an apparatus utilizing heat pipes to transmit heat to and from the magnetic material.
Magnetic refrigerators such as diclosed in U.S. Pat. Nos. 4,459,811 and 4,332,135 both issued to Barclay et al., and U.S. Pat. Nos. 4,408,463 and 4,507,927 both issued to Barclay are known and the four patents are specifically incorporated herein by reference. Such magnetic refrigerators utilized paramagnetic or ferromagnetic material and moved the material in and out of the magnetic field, or by some other means, caused the material to magnetize and demagnetize. Many such magnetic refrigeration devices are operable over wide temperature ranges by staging a plurality of materials listed in the '135 patent. However, all such proposed magnetic refrigerator apparatus depended upon the flow of a fluid to transfer heat from the magnetic material to a heat sink or heat load. This flowing fluid required elaborate seals and pumping mechanisms to insure proper transfer of heat in the desired direction.
U.S. Pat. No. 4,464,903 issued to Nakagome, et al. disclosed directional heat pipes disposed in a stationary mass of magnetic material and emerging from both top and bottom surfaces. A magnet moved closer to and away from the magnetic mass to vary the magnetic field. However due to the thermal addenda resulting from this arrangement of parts and the use of Gd.sub.3 Ga.sub.5 O.sub.12 as the magnetic material, if the magnetic material was initially at 20 K., the heat pipes transferring heat from whatever is to be cooled probably reached temperatures no lower than 5.2 K. during the demagnetization process. This probably prevented the operation of a helium heat pipe. Conversely, if the magnetic material was initially at 4.2 K., the heat pipe transferring heat away from the magnetic material probably did not exceed temperatures of 13.1 K. during the magnetization process. Thus, the hydrogen heat pipe also probably was rendered inoperative. At best, minimal heat transfer would have occurred if the heat pipes operated at all, because of the reduced temperature changes of the magnetic material.
There is, however, an existing need for an efficient refrigeration apparatus which does not depend upon flowing fluid to transfer heat energy in and out of the region where the magnetic material interacts with a cyclically timed varying magnetic field. The instant invention transmits heat through the use of heat pipes thus, eliminating elaborate seals and pumping mechanisms to transfer heat in a desired direction. Furthermore by proper arrangement of parts, the thermal addenda is minimized making it possible for the heat pipes to operate efficiently at their designed temperature.